1. Field of the Invention
The present invention generally relates to an internal EGR parameter estimating device for an internal combustion engine. More specifically, the present invention relates to a technology for calculating the quantity of exhaust gas that blows between the exhaust side and the intake side during the overlap period when both the intake valve and the exhaust valve are open (i.e., the blow-by gas quantity) in a simple and accurate fashion.
2. Background Information
Conventionally, engines are configured to execute exhaust gas recirculation (hereinafter called “EGR”) whereby a portion of the exhaust gas is returned to the cylinders in order to suppress the generation of nitrous oxides (NOx) resulting from higher combustion temperatures.
There are basically two types of EGR arrangements: an external EGR in which the exhaust gas is recirculated through an EGR pipe connected between an exhaust pipe and an intake pipe; and an internal EGR in which the exhaust gas is recirculated without using the EGR pipe. One example of an EGR estimation device is disclosed in Japanese Laid-Open Patent Publication No. 2001-221105 in which the quantity of gas recirculated by internal EGR estimated. The device disclosed in that publication is configured to calculate a basic value of the internal EGR quantity based on the engine rotational speed, the exhaust valve close timing, and the assumption of operating conditions under which the open period of the intake valve and the open period of the exhaust valve do not overlap. When the open periods of the intake and exhaust valves overlap, the internal EGR quantity is calculated by adding to the basic EGR quantity an overlap compensation value that is calculated based on such factors as the amount of overlap and the intake air pressure.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved internal EGR parameter estimating device. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.